docs(exception): complete app.onError example with non-HTTPException fallback

[ramanverse]

Problem

Fixes honojs/hono#2603

The app.onError example in docs/api/exception.md ended with a // ... placeholder, leaving readers with no guidance on how to handle errors that are not an HTTPException. The existing code also used internal twoslash ---cut-start---/---cut-end--- markers to hide the fallback from the rendered docs entirely.

Changes

File: docs/api/exception.md

• Replaced the // ... placeholder and hidden twoslash cut blocks with a complete, visible fallback
• Shows the recommended pattern: log unexpected errors with console.error(err) and return c.text('Internal Server Error', 500)
• Renamed error → err for consistency with Hono's codebase style

Before / After

Before:

app.onError((error, c) => {
  if (error instanceof HTTPException) {
    console.error(error.cause)
    return error.getResponse()
  }
  // ...
})

After:

app.onError((err, c) => {
  if (err instanceof HTTPException) {
    // Return the error response generated by HTTPException
    return err.getResponse()
  }
  // For any other unexpected errors, log and return a generic 500 response
  console.error(err)
  return c.text('Internal Server Error', 500)
})

Impact

Docs-only change. No source code or tests modified.

[yusukebe]

LGTM

[yusukebe]

@ramanverse Thanks.